192 ARCHER, ON STEPHANOSPHERA PLUVIALIS. 
and, apparently following him, Vaupell,* seem to urge that 
an exosmotic action operates upon the young zoospore, in- 
ducing the phenomena described. Cohn likewise,+ in such 
cases (speaking of the zoospores of Vaucheria and Hydro- 
dictyon), where the so-called primordial utricle (outer proto- 
plasmic layer) presents contraction and expansions, seems to 
have arrived at the conclusion that such alterations of figure 
are wholly due to the taking up and withdrawal of water, and 
not to any special inherent contractility. The very interest- 
ing experiments upon Spirogyra, Closterium, &c., which Cohn 
describes, seem to prove only that by the alternate absorption 
and withdrawal of water the cell contents become contracted 
or expanded as a whole, that is, become alternately changed 
in bulk and density; but it does not to me appear that such 
experiments call forth anything like “ rhizopodous” phe- 
nomena; such as those described in this paper, nor will the 
results of such experiments account for them. The former 
(that is, automatic contracility) is, I venture to believe, far 
more likely to be the true solution. Many other similar in- 
stances in zoospores (for instance, Vaucheria), as is well 
known, might be here cited. Yet, in his elaborate memoir 
on Protococcus pluvialis (Kiutz.),{ published previously, the 
latter observer seems to dwell upon the similarity of the con- 
tractile phenomena presented by the primordial utricle of 
that remarkable organism to those shown by Euglena and 
Astasia ; and he bases thereupon certain comparisons of the 
vegetable protoplasm to that of the animal, leading him to 
the conclusion that these are quite analogous, correctly re- 
garding (as I conceive) Protococcus pluvialis as a plant, and 
assuming Euglena to be the animal. However, his own very 
interesting observations on Euglena,§ as well as those of 
others, seem rather to point to the conclusion that this puz- 
zling organism is really a phase of a plant. Hence, as I 
conceive, it seems to have needed such observations as those 
of Dr. Hicks, and that on Stephanosphera here recorded— 
that is to say, evidence of automatic rhizopodous movements 
in undoubted plants—to complete the proof of the similarity 
of the animal and vegetable protoplasm. 
Again, in our search for analogous cases, as regards cells 
which are not zoospores, let us refer to the figures of my 
* Loe. cit. (‘Iagttagelser,’ &c.), p. 29. 
ae Loe. cit. (‘ Untersuchungen tiber d. mikr, Alg. und Pilze’), pp. 228, 
_ ¥ ‘Zur Naturgeschichte des Protococeus pluvialis (Kitz.).” In abstract, 
in Ray Society’s Publication for 1858. 
§ Ibid., p. 733. 
